1. Field of the Invention
The present invention relates to a bus system and a bus sense amplifier.
2. Description of the Background Art
FIG. 21 shows a conventional bus sense amplifier. This is disclosed in Proceeding pp. 637-640 at the Custom Integrated Circuits Conference in May 1994. This bus sense amplifier is of current detection type, in which an NMOS transistor of which gate electrode is connected to the output of data register is turned on, and the current flowing in a PMOS transistor with the diode connection flows into the ground through the NMOS transistor, and this current is detected at high speed by a PMOS current mirror to be converted into voltage. More precisely, supposing the gate width of the NMOS transistor at the data register side to be W, the both currents of the transistors having driving force of which gate width correspond to W and W/2 respectively are compared by the PMOS current mirror.
Hence, when the content of the data register is 0, the current flows through the NMOS transistor with width W, and the both currents flowing in the transistor with gate width W and transistor with gate width W/2 are compared at this time, and the output becomes L level. By contrast, when the content of the data register is 1, current does not flow at the input side, and hence no current and the current flowing in the transistor with gate width W/2 are compared, and the output becomes H level.
In this bus sense amplifier, since the amplitude of the bus BUS is pulled up by the NMOS transistor, its amplitude is (Vdd-Vth) during the precharge period, and does not hike up to Vdd corresponding to the high level of the ordinary CMOS circuit. Hence a bus system of high speed and low power consumption is realized. Herein, Vdd is the supply voltage, and Vth is the threshold of NMOS transistor.
However, in the circuit of conventional bus sense amplifier shown in FIG. 21, penetration current flows into the right side path in FIG. 21, and penetration current also flows into the input side. Hence, the problem is that the effect of lowering the power consumption by lowering the bus amplitude is canceled by the occurrence of those penetration current.
More specifically, in the PMOS current mirror type bus sense amplifier, when the current is pulled in from the register side, a DC current flows in the EVL period, and hence a current of 0.5 mA is consumed per amplifier.